Method for Automatically Producing an Optical Blend Mask

ABSTRACT

A method for automatically producing an optical blend mask arranged in a beam path ( 8 ) of a projector ( 2 ) in a projection system with two projectors ( 2 ), by determining an actual state of the projection system by calibrating and producing an ideal blending, ascertaining an individual distortion of the projector ( 2 ) by using a front or back projection surface ( 11 ), introduced into the beam path ( 8 ), using patterns ( 13 ) from which points are derived, ascertaining the alignment and the position of the front or back projection surface ( 11 ) within a blend mask plane, calculating the optical blending for a partial image, for positioning and/or a transformation of the ideal blending, adapting the ideal blending for compensating a soft focus, applying the ascertained, individual distortion of the projector ( 2 ) to the blending, ascertaining data of the optical blend mask and outputting data for producing the optical blend mask.

The invention relates to a method for automatically producing an optical blend mask which is used in the beam path of a projector in a projection system comprising at least two projectors.

Large-area projections, which are produced by so-called projection systems, are usually composed of several small projections or partial images, with the individual projection channels which produce the partial images being geometrically distorted and blended in a manner adapted to the projection surface. In this way, a correspondingly large-scale homogeneous projection or display on the projection surface can be produced, for example, by using four projectors, which each produce a partial image of the large-area projection.

The information required for the distortion and blending are determined, for example, by a so-called calibration of the overall projection or the projection system. For this purpose, predefined patterns are projected onto the projection surface. These patterns mark points on the projection surface or are designed so that points can be derived therefrom. Points derived in this way can be obtained from two intersecting lines or, for example, from one corner of a flat geometric figure.

The spatial positions (X, Y and Z coordinates) of these marked points are measured, for example, with two cameras. Based on this point model, the overlap of the individual projectors can be determined at any point on the projection screen and a blending for each projector involved in the production of the large-area projection can be derived therefrom. This blending is realized by the optical blend mask to be produced automatically.

According to the prior art, the video signals of the individual video channels of the projectors, which are required for each partial image generation, are varied after image formation by using suitable methods for distortion and blending of the video signals. Subsequently, the thus-changed signal is supplied to a projector as an input signal, which produces the corresponding partial image on the projection surface. This process of signal processing or signal change is usually performed for each of the video channels involved in generating the projection, that is, for each partial image.

Thus, the changes of the video signals necessary for generating the large-area projection on a projection surface, for example, to adapt to the given projection surface and/or to a blending, are directly applied to the input signal of each projector and affect the projection of the displayed partial images.

Alternatively, it is known that blending can be realized by using optical blend masks, which are arranged in the beam path in front of the respective projector.

Regardless of the selected method for the distortion and/or the blending, a recalibration of the projection system is required in the event that one or more projections or projection channels change, for example, due to a change in the position of one or more projectors. The distortion and the blending must also be corrected with the new data of the calibration. In addition to a change in position, a recalibration and adjustment of the projection system is usually required even when replacing a lamp in a projector.

Most projectors are in principle unable to project images or partial images that are displayed in an image part having no brightness, i.e. which are completely black. This is due to the fact that the light source in the projector is always on and that the light path cannot be completely blocked. As a result, projectors have a so-called residual brightness, for example when displaying a black screen.

Large-area projections using multiple projectors are usually generated by at least partially overlapping the partial images in their peripheral areas, thereby producing a so-called blend zone. When such image areas overlap in the blend zone, the residual brightness of the different projectors is unfavorably superimposed. In particular, when representing very dark image areas in the overlaps of the partial images, the resulting residual brightness is perceived by a viewer as very disturbing, since the blending has no effect on the residual light.

One solution to the problem of this residual brightness is to reduce or prevent the residual light projection by using an optical blend mask in the light path. When using, for example, four projectors in a large-area projection, four optical blend masks must be provided, i.e. one blend mask for each projector.

In the prior art, these optical blend masks are produced strictly according to a design or according to data from corresponding test projections. Since the real projection system is always different from the design or from an ideally planned projection, the results produced with these optical blend masks are not always satisfactory.

The reason for the limited functionality of such optical blend masks is, on the one hand, based on the fact that it is very difficult in practice to construct a projection system exactly according to a given design. On the other hand, a so-called individual distortion of a projector caused by inaccuracies in the manufacture of the lenses or lens pairs of a projector cannot be taken into account at all or only with a substantial design effort.

EP 1 422 939 A2 discloses a multi-channel projection system and a method for realizing large projection surfaces. To provide a low-cost, large-area projection, a multi-channel projection system with at least two side-by-side or stacked projectors is proposed, with a single projector each projecting part of the image. The described projection system is characterized in that an identical input signal representing the projected total image is applied to the at least two projectors, wherein the pixel resolution of the image to be displayed is greater than the resolution of the projection screens of the at least two projectors and means are included for electronically moving the image on the respective panel of the projectors, such that the partial images projected by the individual projectors together produce the total image to be projected.

WO 2012/076706 A1 discloses an optical blend mask suitable for use in representing an overall picture composed of several overlapping individual images. The mask includes an arrangement of elongated sliding elements disposed side-by-side on a carrier, with each sliding element being disposed for moving independent of one another along an axis. It is intended to arrange one or more of these masks, for example, in a light beam of a projector and to thus change the transmission of the light.

U.S. Pat. No. 6,513,938 B2 relates to a projection system with a plurality of image projection means, in which overlapping partial images projected by the plurality of image projection means are arranged in such a way that an overall image is produced. The object of this document can be seen to provide a projection system, which makes it possible to provide an overall picture composed of a plurality of partial images with a virtually uniform luminance level over the entire projection area.

The arrangement includes a plurality of image projection means having one or more intercepting plates arranged between the image projection means and the projection surface, a luminance detection means, a displacement calculating means and a control means.

It is disclosed, for example, to use an L-shaped intercepting plate in front of one of four image projection means, which arranged in front of the image projection means for displacement in order to adjust the required luminance. It is also intended to automate this displacement by using a control signal produced by the control means and corresponding drive means which are adapted to change the position of the intercepting plate in front of the image projection means in the vertical and horizontal directions.

EP 1 613 071 A1 disclose a method for providing attenuation of the luminous intensity of an image in an edge region of one of a plurality of tiled partial images in a total projection displayed by a projection display system. In particular, the document relates to a method for obtaining improved blending of tiled images displayed by a projection display system. The method provides both good black-level blending and high flexibility.

A first light intensity is changed with an electronic soft-edge device over a first fraction of the edge region from a first intensity value to a first fraction of the first intensity value and a gradual change of the first light intensity by an optical soft-edge device over a second fraction of the edge region from a second fraction of the first intensity value to a third fraction of the first intensity value. The optical attenuation of the light intensity of the image should here be substantially constant in the first fraction and in the second fraction of the edge region. The optical soft-edge device includes at least one mask.

In a particular embodiment, a third fraction is also provided which is arranged between the first and the second fraction and in which both the electronic soft-edge device and the optical soft-edge device are used for influencing the light intensity of the third fraction.

The prior art thus has the disadvantages that no optimal compensation for the problem associated with residual brightness occurring in the blend zones of a large-area projection is provided. In particular, compensation by using an optical blend mask cannot be adapted automatically to the real projection system, which always differs at least partially from a planned design, and/or to existing distortions of the projectors, which likewise always occur in practice. Alternatively, it is only possible to manually adjust the optical blend masks and the blending. For this purpose, elements that influence the propagation of the light can be introduced into the beam path, for example in the region of the blend masks. Such an adjustment of the mask is a manual adjustment operation, which requires an experienced professional and is subject to subjective evaluation.

The object of the invention is to provide a method for producing an optical blend mask, with which an optical blend mask is produced automatically, which is adapted to an actual individual state of a projection system as well as to distortions caused by at least one lens of a projector.

The object is achieved by a method having the features according to claim 1. Further developments are specified in the dependent claims 2 to 8.

According to the present invention, it is provided that one or more optical blend masks are calculated and produced based on data determined during calibration of an actual state of a projection system. Each optical blend mask produced in this manner is after its production arranged or mounted at a defined location in the beam path of an associated projector.

The uniqueness of the method according to the invention is that blending is calculated with the aid of projected points located within patterns whose spatial position is measured and which are projected onto the projection surface and hence also imaged on the projection surface located in the plane of the blend mask, and this calculated blending is transmitted or printed onto an optical blend mask located in the beam path of the projector. For this purpose, the position of a frame receiving the optical blend mask to be produced or of the frame with a front or rear projection surface is measured in the beam path. To realize this measurement, the frame and/or the front or rear projection surface is provided with so-called measuring marks. The position of the blend mask and the blend characteristic on the automatically produced mask can be calculated therefrom.

Optical blend masks produced in this way significantly reduce or eliminate the disadvantage of optical blend masks calculated and fabricated according to a given design and do not require a manual setup.

This is true both for the inaccuracy of the optical blend mask, which results from the fact that it is practically very difficult to construct the projection system exactly as designed, as well as for the proportion of the inaccuracy caused, for example, by an individual distortion of each projector-lens pair.

Either inaccuracies or disturbances are taken into account in a design of the optical blend mask based on data produced by the calibration, i.e. by a measurement of the real actual state of the projection system. In this way, an optical blend mask is produced, which is individually adapted to the associated projector and its position with respect to the projection surface or the projection system.

To produce the data necessary for the production of the optical blend masks, the following process steps explained below are carried out:

In the first method step, the blending is calculated for each individual projection based on a measurement of the overall projection. The blending is calculated in relation to the image signal. In a subsequent method step, the distortions of all the projector-lens pairs are measured in a so-called blend mask plane, which is located in a plane, typically orthogonal to the optical axis, immediately in front of the respective projector-lens pair. This makes it possible to determine at which location and with which distortion the calculated blending must be placed as an optical blend mask.

For this measurement of the distortion, a front or rear projection surface is arranged in front of each projector at a location in the beam path of the projector (blend mask plane) where the optical blend mask to be produced is used after its production.

Several optical markers are located on this front or rear projection surface. The front or rear projection surface is respectively received by a holder or frame, which is arranged in front of the respective projector. The front or rear projection surface is removable from the holder and can always be brought exactly in the same position by the holder which is firmly connected to the projector or to another fixed point. After completion of the optical blend mask, the optical blend mask is inserted in the holder or frame at the location of the front or rear projection surface.

The markers on the frame form a local reference coordinate system. The distortion of the projector is determined in this coordinate system with a calibration. At the same time, the position of the optical blend mask within the local reference coordinate system is determined.

To perform the calibration, patterns from which points can be derived are projected onto the front or rear projection surface arranged in the blend mask plane, which are recorded with a camera and provide an association of the front or rear projection surface with the local reference coordinate system.

At least one such camera can be arranged, for example, in front of or behind the blend mask plane and aligned with the front mask or rear projection surface arranged in the blend mask plane.

The data of an optical blend mask calculated with the method are transferred by a suitable technique to a transparent support medium, which may be for example a foil or glass.

In an alternative embodiment, the data obtained in the method may be used, for example, to control a display arranged in front of the projector at the location of the optical blend mask. For this purpose, any display transmitting the light from the projector can be used. As with a manufactured optical blend mask, the data define a brightness value of pixels in the display, with a reduction in the brightness value resulting in an attenuation of the transmitted light at that location. Such a display can, for example, be a so-called Digital Information Display (DID), a transparent Liquid Crystal Display (LCD), or a transparent Organic Light Emitting Diode Display (OLED).

The produced optical blend masks contain registration marks which correspond exactly to the markers of the frames. The optical blend masks can thus be fixed in the frame very precisely and thus assume an exact position in the reference coordinate system.

The optical blend masks are pushed into holders located at a fixed position in front of the projector. By using this transitive, relative position specification, the mask is positioned exactly in the projection path, i.e. in the beam path of the respective projector in front of this associated projector.

Process Flow:

1. Measuring the projection system and generating the ideal blending

2. Arranging a front or rear projection surface in frames in front of a projector:

-   -   a) Projecting patterns from which points can be derived,     -   b) Recording the points derived from the pattern, for example by         using a camera,     -   c) Determining the position of the recorded points in the local         reference coordinate system,     -   d) Association with the projected points,     -   e) Calculating the distortion of the projector.

3. Calculation of the optical blending:

-   -   a) Positioning and/or transforming the ideal blending onto the         blend mask layer,     -   b) Filtering or adapting the ideal blending to compensate for         the soft focus in the light path, since the optical blend mask         in the blend mask plane is not in the focal plane of the         projector,     -   c) Optional iterative optimization of the optical blend mask         produced according to steps a) and b), wherein the ideal image         of the blending on the projection surface (blend result) is         simulated and compared with blending expected using the         previously created optical blend mask in order to reduce the         deviations between the ideal image of the blending and the         expected blending,     -   d) Application of the distortion of the projector as determined         in point 2 to the blending.

4. Outputting the generated data for producing the optical blend mask.

In this case, ideal blending is to be understood as blending which would allow an absolutely error-free projection of a partial image. The method automatically determines data that can be used to produce an optical blend mask, which very closely approximates the characteristics of the ideal blending.

The iterative optimization in point 3 c is necessary to reduce disturbances in the representation of the large-area projection 5, which are caused by diffraction effects and/or distributed light sources.

Further details, features and advantages of embodiments of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings, which show in:

FIG. 1 a schematic diagram of a large-scale projection onto a curved projection surface with several projectors,

FIG. 2 a diagram of the partial images of the large-area projection,

FIG. 3 a diagram of possible signal processing steps for generating of partial images of a large-scale projection,

FIG. 4 a large-area projection by using two projectors with a blend zone located between the produced partial images,

FIG. 5 a diagram of four optical blend mask masks, which are used in generating a large-area projection using four projectors,

FIG. 6 one of several projectors for producing a large area projection with an optical blend mask arranged in the beam path of the projector, and

FIG. 7 the positioning of a front or rear projection surface in a frame in the beam path of a projector in front of a projection surface.

FIG. 1 shows a projection system 1, which by way of example includes four projectors 2 a, 2 b, 2 c, 2 d. Each projector 2 a, 2 b, 2 c, 2 d produces a partial image 4 a, 4 b, 4 c, 4 d on the projection surface 3, which together produce a large-area projection 5. The generation of this large-area projection 5 takes place in such a way that a blend zone 9 is formed between two adjacent partial images 4 a, 4 b, 4 c, 4 d, in which image portions of the adjacent partial images 4 a, 4 b, 4 c, 4 d are superimposed. The image signals or video signals of the partial images 4 a, 4 b, 4 c, 4 d required for the control of the projectors 2 a, 2 b, 2 c, 2 d are generated in a suitable central signal generating unit, which will not be described in detail, since it does not affect the disclosure of the present invention.

The required partial images 4 a, 4 b, 4 c, 4 d are initially generated in the signal generation unit in such a way that the large-area projection 5 can be projected without errors when displayed only on a flat projection surface 6, which is shown in FIG. 1 solely for simplifying the illustration.

To enable an error-free representation on the curved projection surface 3, the entire projection system 1 is calibrated. In this calibration, data is produced which makes it possible to distort the partial images 4 a, 4 b, 4 c, 4 d in such a way that they are displayed to a viewer on the curved projection surface 3 and perceived by the viewer to be true to the original, without undesired displacements or distortions.

In addition to this distortion of the partial images 4 a, 4 b, 4 c, 4 d, the signals of the partial images 4 a, 4 b, 4 c, 4 d are also changed for superposition in the blend zones 9 with sufficient accuracy and are hence can no longer perceived by the viewer as individual or separate partial images 4 a, 4 b, 4 c, 4 d, thus visually displaying a coherent large-area projection 5. For this purpose, blending, i.e. an adjustment of the brightness of the partial images 4 a, 4 b, 4 c, 4 d within the blend zones 9, must be performed.

FIG. 2 shows the partial images 4 a, 4 b, 4 c, 4 d of the large-area projection 5 in respective individual images. As can be clearly seen, for example, in the partial images 2 a and 2 b, the partial images 2 a and 2 b can produce a fault-free image only when they partially overlap along their common side. It can also be clearly seen in the example of the partial images 4 a and 4 b that the eye of the illustrated duck must be brought into agreement in order to obtain an error-free large-area projection 5.

FIG. 3 shows various process flows for distorting and blending the partial images 4 a, 4 b, 4 c, 4 d. The illustration shows the sections Image Generation 15, Distortion 16, Blending 17, Projection 18 and the respective light path 8.

In the first variant (variant 1), after the image or video signals to be displayed are generated in an image generation unit 19, for example in a computer, the partial images 4 a, 4 b, 4 c, 4 d in the section 16 are distorted for adaptation to the conditions of an uneven projection surface 3. This adaptation takes place, for example, in a special distortion unit (warp unit) 20 or in a graphics card 21. Subsequently, a blending method is used in section 17 before the adapted signals of the partial images 4 a, 4 b, 4 c, 4 d in section 18 are each projected on the projection surface 3 with respective projectors 2 a, 2 b, 2 c, 2 d via the light paths 8. The blending can be realized in a special blend unit 22 as well as with a graphics card 21.

In the second variant (variant 2), the image or video signals to be displayed are already generated by taking into account the distortion as well as the blending in a single step in a suitable unit, such as a computer. This unit or this computer represents the image generation unit 19, the distortion unit (warp unit) 20 and the blend unit 22 and applies the distortion of the signal to be performed in section 16 and the blending to be performed in section 17. The thus generated signal of a partial image 4 a, 4 b, 4 c, 4 d is again projected in section 18 onto the projection surface by using a projector 2 a, 2 b, 2 c, 2 d via the light path 8.

In the third variant (variant 3), the image or video signals to be displayed are generated in an image generation unit 19, such as a computer or similar unit suitable for data processing. The signal produced in this way is supplied to a distortion unit (warp unit) 20 or a graphics card where the signal experiences in section 16 a corresponding distortion for adaptation to the projection surface 3. This distorted signal is projected in section 18 by using a projector 2 a, 2 b, 2 c, 2 d via the light path 8 onto the projection surface 3, wherein each projector 2 a, 2 b, 2 c, 2 d has an optical aperture mask 7 a, 7 b, 7 c, 7 d arranged in the beam path 8 immediately in front of a projector 2 a, 2 b, 2 c, 2 d, which realizes the blending of the signal.

In the fourth variant (variant 4), the image or video signals to be displayed are produced by an image generation unit 19, for example in a computer, in which the signal also experiences a corresponding distortion. The computer thus also represents the operation of the distortion unit (warp unit) 20. In this variant, too, the distorted signal is subsequently projected in section 18 onto the projection surface 3 by using a respective projector 2 a, 2 b, 2 c, 2 d via the light path 8, with an optical blend mask 7 a, 7 b, 7 c, 7 d, which implements blending of the signal, arranged in the beam path 8 immediately in front of each projector 2 a, 2 b, 2 c, 2 d.

FIG. 4 shows a large-area projection 5 using two projectors 2 a and 2 b. The partial images 4 a and 4 b produced by the projectors 2 a and 2 b are projected onto the projection surface 3, creating between the partial images 4 a and 4 b a blend zone 9, in which the partial images 4 a and 4 b overlap. As shown in FIG. 4, not only the image contents of the partial images 4 a and 4 b overlap in the blend zone 9, but also the respective brightness of the partial images 4 a and 4 b. As already described, this overlap of the respective brightness must be compensated by the blending so that the overlap can no longer be perceived by the viewer as disturbing.

For this purpose, suitable methods are used for blending, i.e. for influencing the brightness of the image or video signals of the partial images 4 a and 4 b in a suitable unit such as a computer or a graphics card. Alternatively, an optical blend mask 7 a and 7 b can be used in the beam paths 8 of the respective projectors 2 a and 2 b. Such optical blend masks 7 a and 7 b are not shown in FIG. 4.

FIG. 5 shows four exemplary optical blend masks 7 a, 7 b, 7 c, 7 d. These four optical blend masks 7 a, 7 b, 7 c, 7 d are intended for a projection system that produces a large-area projection 5 composed of four partial images 4 a, 4 b, 4 c, 4 d by using four projectors 2 a, 2 b, 2 c, 2 d.

The optical blend masks 7 a, 7 b, 7 c, 7 d have areas along two adjacent edges which have dark fields and extend in the shape an “L”. By using these dark fields, the brightness of the projected partial images 4 a, 4 b, 4 c, 4 d on the projection surface 3 is reduced in the blend zones 9, producing a uniform brightness when the partial images 4 a, 4 b, 4 c, 4 d are superimposed. This process of blending is achieved by varying the opacity in the L-shaped fields. The masks 7 a, 7 b, 7 c, 7 d remain translucent outside the opaque areas that are not located within the blend zone 9.

FIG. 6 shows part of a projection system 1. The example shows the projector 2 b of a projection system 1 having four projectors 2 a, 2 b, 2 c, 2 d. This projector 2 b projects the partial image 4 b, which represents the upper right-hand portion of the large-area projection 5, onto the curved projection surface 3. In the illustration of FIG. 6, an optical blend mask 7 b is arranged in the beam path 8 of the projector 2 b in a so-called blend mask plane. For affixing the optical blend mask 7 b, for example, a frame may be provided, in which the optical blend mask 7 b can be arranged. This frame is preferably fixedly connected to the projector 2 b via a holder. The frame and the holder are not shown in FIG. 6.

FIG. 7 shows positioning of a front or rear projection surface 11 in a frame 10 in the beam path 8 of a projector 2 in front of a projection surface 3. The illustration shows a, for example, U-shaped frame 10 arranged in front of the projector 2, which is suitable both for receiving a front or rear projection surface 11 and for receiving an optical blend mask 7 produced according to the process flow.

The frame 10, which is not limited to the illustrated shape, may for example have a groove into which the front or rear projection surface 11 as well as the mask 7 can be inserted. The frame 10 is firmly connected to the projector 2 by way of an unillustrated holder or to another fixed point and is fixed in its position in this way. Marks 12 which define a local reference coordinate system are arranged on the frame 10. The position of the front or rear projection surface 11 and of the optical blend mask 7 is defined in this local reference coordinate system.

FIG. 7 shows the frame 10 with a front or rear projection surface 11 onto which patterns 13 are projected. Preferably, these patterns 13 can be points whose relative position with respect to a local reference coordinate system is determined by using a camera recording the points and by an unillustrated computing and control unit.

An imaged projection surface 14, which is generated when the projector 2 projects a partial image 4 onto the projection surface 3, is shown on the front or rear projection surface 11 arranged in the beam path 8 of the projector 2. The position and orientation of this imaged projection surface 14 located in the blend mask plane is detected in the blend mask plane in accordance with the method and serves to precisely align the optical blend mask (7) within the image mask plane when the data for the optical blend mask (7) are generated.

LIST OF REFERENCE NUMBERS

-   1 projection system -   2 a, 2 b, 2 c, 2 d projector -   3 projection surface -   4 a, 4 b, 4 c, 4 d partial images -   5 large-area projection -   6 flat projection surface -   7 a, 7 b, 7 c, 7 d optical blend mask -   8 beam path -   9 blend zone -   10 frame -   11 front or rear projection surface -   12 mark -   13 pattern -   14 imaged projection surface -   15 image generation -   16 distortion -   17 blending -   18 projection -   19 image generation unit (Personal Computer PC) -   20 distortion unit (warp unit) -   21 graphics card -   22 blend unit 

1. A method for automatically generating an optical blend mask (7), arranged in the beam path (8) of a projector (2) in a projection system (1) comprising at least two projectors (2), comprising the steps of: determining an actual state of a projection system (1) by a calibration and by generating an ideal blending, determining an individual distortion of the projector (2) by using a front or rear projection surface (11) inserted in the beam path (8) of the projector (2) using patterns (13) from which points are derived; determining the orientation and the position of the front or rear projection surface (11) within a blend mask plane with respect to a local reference coordinate system, calculating the optical blending for a partial image (4) to be projected by the projector (2) in such a way that the ideal blending is positioned and/or transformed on the blend mask plane, adapting the ideal blending to compensate for a soft focus in the beam path (8), applying the determined, individual distortion of the projector (2) to the blending, and determining data of the optical blend mask (7) which are outputted for generating the optical blend mask (7).
 2. The method according to claim 1, wherein the determining the individual distortion of the projector (2) includes the following method steps: projecting patterns (13), from which points are derived, recording the points derived from the pattern (13) by using a camera, with the position and alignment and/or orientation of the camera in the local reference coordinate system being known, determining the points in the local reference coordinate system, assigning to the projected points, calculating the distortion of the projector (2).
 3. The method according to claim 1, wherein the calculation of the optical blending also comprises the method steps of iteratively optimizing the data of the produced optical blend mask (7), wherein the ideal imaging of the blending on the projection surface (3) is simulated and compared with a blending expected using the data of the previously created optical blend mask (7) so as to reduce the discrepancies between the ideal image of the blending and the expected blending.
 4. The method according to claim 1, wherein the data for generating the optical blend mask (7) include information about the number of pixels arranged horizontally and vertically in the optical blend mask (7) and their intensity on the blend mask (7), with which a brightness reduction is performed.
 5. The method according to claim 1, wherein the optical blend mask (7) produced according to the determined data is used at the location in the beam path (8) of the projector (2) at which the front or rear projection surface (11) was positioned when determining the individual distortion of the projector (2).
 6. The method according to claim 1, wherein the data for generating the optical blend mask (7) are determined for two or more optical blend masks (7).
 7. The method according to claim 1, wherein the outputted data of the optical blend mask (7) are used to control a printing method for producing a printed optical blend mask (7).
 8. The method according to claim 1, wherein a display through which the light from the projector (2) is transmitted and which images the optical blend mask (7) is controlled with the outputted data of the optical blend mask (7). 